The worldwide trade in illegal drugs sold over the internet has surged, according to the UN's drug watchdog.

Dangerous drugs are being sold without prescription in a virtual marketplace that is difficult to control, says the International Narcotics Control Board.

In its annual report, it says that 90% of online drugs sales take place without a medical prescription.

Legal suppliers were fuelling the trade, it says, by providing unlicensed internet pharmacies with drugs.

The INCB warn the web is increasingly a source of illicit drugs for children offering access which is not restricted by age.

"The illicit trade over the internet has been identified as one of the major sources for prescription medicines abused by children and adolescents in certain countries such as the United States," it says.

Mind-altering drugs

The US, it says, remains the largest market in the world for illegal drugs with 8.2% of its population of 293 million people using them.

The most common sales are of mind-altering substances such as amphetamines.

"Billions of [doses of] controlled substances - some of them highly potent drugs such as oxycodone, equivalent to morphine, and fentanyl, which is many times stronger than morphine - are being sold by unlicensed internet pharmacies."

The INCB called for better co-operation between governments, international organisations and the pharmaceutical industry.

The report also highlighted that drug abuse and trafficking was a growing problem in many African countries.

It cited a marked increase in the use of intravenous drugs - such as heroin - in eastern and southern Africa and said this could have serious ramifications for the spread of HIV and Aids.

The INCB also said it was worried by Afghanistan's opium production.

The country now supplies three-quarters of the world's heroin as well being a major source of cannabis resin.